French army officer and diplomat, better remembered for his exploits in love affairs than for his public service.

At the time of his birth, his mother, Adèle Filleul, was the wife of the Comte de Flahaut, but Charles was generally recognized to be the offspring of her liaison with Talleyrand. During the Revolution, in 1792, his mother took him into exile, and they remained abroad until 1798.

He entered the Army in 1800 and received his commission after the Battle of Marengo. He became aide-de-camp to Joachim Murat (and the lover of Murat's wife, Caroline, Napoleon's sister) and was wounded at Enns, in Austria, in 1805. In Warsaw he met Anna Poniatowska, Countess Potocka, who became his mistress. He served in Portugal (1807), in Spain (1808), and then in Germany. Meanwhile, Countess Potocka had established herself in Paris, but Flahaut was now the lover of Napoleon's daughter-in-law Hortense de Beauharnais, queen of Holland, by whom he had a son, known later as the Duc de Morny. Flahaut fought in the Russian campaign of 1812 and in 1813 became aide-de-camp to Napoleon.

After Napoleon's abdication in 1814 he was placed on the retired list. The Hundred Days brought him into active service again, but his mission to Vienna to secure the return of Marie-Louise failed. He was saved from exile by Talleyrand's influence. Later he settled in England, where in 1819 he married Margaret Elphinstone, afterward Baroness Keith in her own right. The French ambassador opposed the marriage, and Flahaut resigned his commission.

Flahaut returned to France in 1827, and in 1831, under the July Monarchy, he was made a peer of France. He remained intimately associated with Talleyrand's policy and was ambassador in Berlin for a short time in 1831. He was afterward attached to the household of Ferdinand, duc d'Orléans. He was ambassador to Vienna from 1841 to 1848, when he was dismissed and retired from the army. After the coup d'etat of 1851 he was again actively employed and from 1860 to 1862 was ambassador in London.